Disclaimer: If you attempt any of what you see from my post, you do so at your own risk. The following is a summary of my experience.The Car: 2002 Maxima SETransmission: 6 speed, HLSD, RS6F51AMileage: 174,000 mi. (approx.)Situation: November 1st, 2014. I jumped in the Maxima, running late to a funeral in Tennessee. Pushed clutch to floor and started it. I could not get gear shifter out of third gear no matter how hard I tried. Something was obviously broken in the transmission.
After a lot of online research, I purchased a 29,066 mile 6 speed, HLSD transmission from a 2006 Nissan Sentra Spec-V (p/n RS6F51H) from http://car-part.com/. Kindly gentlemen cargo shipped it from a junkyard in Arkansas to my door step in North Alabama for $XXX (will update when I remember it). The following were the only differences in the two transmissions: (1) bellhousings were different, (2) final drive ratio were different (3.812 vs 4.133), (3) Maxima  1st & 2nd gear dual synchro, SpecV - 1st gear dual synchro, 2nd gear triple synchro.To Do List:
(1) DOCUMENT EVERYTHING WITH PICTURES!!!
(2) On RS6F51H transmission, swap to Maxima bell-housing
(3) On RS6F51 transmission, swap out SpecV final drive for Maxima final drive
(4) While Im at it, install Fidanza Lightweight Flywheel and RalcoZ Lightweight Underdrive Pulley

Work Setup:
- Set each transmission on cardboard covered work bench side by side (cardboard to protect mating surfaces on transmission and soak up any grease/oil/fluids)
- For fasteners, blow up and print out FSM pages and glue to cardboard. Poke fasteners through on board where you take them out of transmission
- Take off parts from each transmission at same time, label in Ziploc bag
- For large parts, label and place in its own cardboard box
- Clean as you go (scrape off gasket material, use acetone/cloth) to clean
- Follow both factory service manuals for breakdown/buildup